In making foundation and land reinforcement excavations, self-propelled drilling machines are generally used, having a frame on wheels or a support track, lifting winches for excavation accessories and a turret rotating on fifth wheel coupled to the support track and comprising a cabin and control accessories. The rotating turret is generally provided with a power unit, such as a thermal motor or an electric motor for the cabin, for the control accessories and typically for the hoisting winches.
The machine comprises a tower provided with sliding guides on which a rotary table (in the sector also named as “rotary”) moves linearly associated with the excavation accessories of the machine, for example a string of rods or an excavation tool. The rotary table, in particular, receives power, for example hydraulic or electric power, from the power unit and converts it into a rotary movement adapted to move the excavation tools.
The tower is superiorly delimited by a head comprising a plurality of pulleys for returning one or more cables, through which the hoisting winches located on the turret or on the tower itself raise or lower the excavation accessories. The latter are generally axially released but not radially from the rotary table that has an independent raising/lowering system.
In cases in which very high excavation depths are required, the technical solution typically used is to apply the excavation tools to a string of telescopic rods (also referred to in the industry as “kelly”). This string of rods generally consists of multiple rods of decreasing section axially sliding within each other and capable of transmitting to each other the rotary motion and the thrust forces required to advance.
The strings of telescopic rods are generally divided into two types, friction rods and mechanical locking rods.
In friction rods, the torque between the rods is normally transmitted through longitudinal strips welded along the elements that make up the rod, both internally and externally, in order to engage with each other.
The transmission of the axial thrust between the rods therefore takes place by means of the friction between the strips of the rods that is generated in the presence of torque.
The rotary table then has a coupling sleeve also provided with a plurality of strips adapted to engage with the corresponding strips of the outermost rod of the string.
In this way, the outermost rod of the string of rods receives the rotary motion from the rotary table through the engagement between the strips of the sleeve and the outer strips of the rod, while the axial thrust transmission takes place by means of the friction between the strips of the sleeve and those of the outermost rod that is generated in the presence of applied torque. In the absence of applied torque, the rods are axially mutually slidable and the entire string is slidable with respect to the rotary table and is moved by a suitable flexible element, preferably by cable.
In the case of mechanical locking rods, seats are generally formed on the outermost rod of the string, at the top, at the base and sometimes also in intermediate position, where the strips of the sleeve of the rotary table are engaged, thus remaining axially locked. In this way, both the torque and the thrust can be transmitted through a stop with mechanical abutment on the strips and not only by friction. When the strips of the sleeve are engaged in the seats of the outermost rod, it is axially constrained to the rotary. Through a rotation of the rotary table in the opposite direction, the strips of the sleeve can be disengaged from the seats of the rod, thus making the rod slidable relative to the rotary. For transmitting torque and thrust between the rods, the system is the same: a sleeve is formed on the bottom of each rod with strips facing inwards, which engage in the seats of the innermost rod.
During the excavation, the rods in the string are progressively extracted with the descent. By descending deeper, the innermost rods continue the descent until reaching a limit position in which they are completely extracted and stop in mechanical abutment on the respective outermost contiguous rods, while the outermost rod of the string is in abutment against the rotary.
At the end of the excavation step, in order to extract the tool from the ground it is necessary to return the string of rods to the retracted configuration of minimum length. This is possible through the actuation of a winch, generally referred to as main winch, typically mounted on the turret whose cable after being returned on the tower head connects to the upper end of the innermost rod of the string of rods that makes up the kelly rod. The winding of the cable on the drum of the main winch causes the raise of the innermost rod, which at the end of its stroke progressively drags the intermediate rods and then progressively the more external ones.
A dedicated system then allows the sliding of the rotary table on the tower. This dedicated system may comprise a hydraulic cylinder, for example of the long-stroke type or of the multi-extension type; in this case, the rotary table can be moved along the first lower half of the tower. Alternatively, the dedicated system may comprise a further winch, in the sector referred to as pull-down winch that allows the sliding of the rotary table by the entire length of the tower. Typically, the pull-down winch, when present, is mounted almost exclusively on the tower and not onto the turret of the machine and is returned on the tower ends to exert pull and thrust forces on the rotary.
In order to reduce the oscillations and the front and lateral deviations of the string of telescopic rods with respect to the tower during the excavation, there may be a rod guide head sliding on the tower and connected to the upper end of the outermost rod of the string. This connection allows the rotation of the strings but prevents the relative axial sliding between the string and the rod guide head which is then dragged by the string of rods when the latter slides with respect to the tower. The rod guide head performs a function of containment of the radial oscillations of the kelly rod ends, especially when executing inclined or not perfectly vertical excavations.
With particular reference to FIGS. 1A and 1B, they show a known type of drilling machine 100, provided with a kinematism 2, preferably parallelogram, for moving a guide tower 5 with respect to a rotating turret 3 mounted on a self-propelled carriage 4. The turret comprises a control cabin for the operator. Actuating kinematism 2 can allow moving tower 5 both for adjusting the drilling height with respect to the fifth wheel center, and for adjusting the inclination with respect to the ground level. Actuating the parallelogram kinematism 2 allows translating a tower 5 between two positions at different working radius, keeping the inclination constant, or allows the raising or lowering of tower 5, as well as limited movements of lateral inclination, or swing, by adjusting the inclination thereof with respect to the ground level. These movements are made possible also through a swivel joint 6, such a cardan joint, interposed between tower 5 and kinematism 2. On tower 5 there is a rotary table, or rotary 10 provided with a pull push system 11 per se known. A drilling assembly, such as a string of telescopic rods or kelly 12 is placed through the rotary table 10.
The string of telescopic rods 12 is guided in the lower part by the sleeve of the rotary table 10 and in the upper part by a rod guide head 13. An excavation tool 15, which may consist, for example, of a bucket or a screw auger, is fixed to the lower end of the innermost rod of the string of rods 12 so as to receive torque and thrust from said rod.
The movement of the telescopic rods 12 occurs through a winch 8, also referred to as main winch, carried by turret 3 of the machine and configured to allow the winding or unwinding of a traction element 9, such as a cable, which is attached to winch 8 and, after being returned on head 7 of the guide tower, is constrained to the innermost rod of the string of rods 12. In particular, the connection between cable 9 and the innermost rod of the string takes place through the interposition of a swivel joint 14 of a known type. The swivel joint 14 has the function of preventing the transmission of torque between the inner string of the string of rods 12 and cable 9 of the winch, thus preventing the cable from being dragged in rotation by the rotary motion of the rods, and thus preventing the cable from twisting.
FIG. 2A shows a sectional view of the string of rods 12 and of the swivel joint 14 that permits to visualize how the connection between cable 9 and the inner rod is implemented through joint 14. FIGS. 2A and 2B show the string of rods in a condition in which the innermost rod 12A is completely extracted with respect to the immediately outermore rod 12B and with the respective strips in mechanical abutment in order to transmit the torque between the two rods. The inner rod 12A is provided at its upper end with a connection with a seat for a pin designed to connect the swivel joint 14 with the rod. The swivel joint 14 has a substantially cylindrical shape and consists of two parts, a lower half-joint 14A and an upper half-joint 14B, which are axially constrained to one another in the direction of the longitudinal axis of the joint but which are released in rotation, being able to rotate relative to one another about the longitudinal axis of the joint, due to the presence of special bearings interposed between the parts. The lower half-joint 14A is provided with connections for connecting to the upper connection of rod 12A via a hinge pin. Joint 14 is therefore tilting with respect to the connection of the inner rod 12A. The upper half-joint 14B is provided with connections for connecting to the terminal of cable 9 via a hinge pin. Joint 14 has a suitable diameter, preferably smaller than the diameter of rod 12A in order to be insertable within all the telescopic rods that make up string 12, following the sliding of the inner rod without scraping or contacting the outer rods. When cable 9 is tensioned, the swivel joint 14 is arranged with its axis aligned and substantially matching the longitudinal axis of the string of rods 12. When the rods are set in rotation, the lower half-joint 14A rotates integrally with the rods, while the upper half-joint 14B does not rotate and does not transmit rotations to cable 9.
When executing foundation piles using a known type of machine 100, the operator must pay particular attention during all the steps of the excavation and especially during the rotation steps of the rods, to keep cable 9 tensioned to ensure that the swivel joint 14 remains coaxial with the same rods. In fact, if the cable underwent a loosening greater than a minimum acceptable value, the swivel joint 14, being tilting with respect to the connection of rod 12A, would tend to arrange itself inclined and to come into contact with the inner walls of the other rods, thus becoming damaged and also damaging cable 9.
The excavation generally has a first step in which the machine is positioned in the proximity of the pre-hole, or the excavation location indication peg and by adjusting the kinematism, the excavation tool is positioned on the axis of the hole to be made. A plurality of subsequent excavation steps is then carried out; in fact, during the excavation, the excavation tool fills up or charges with the excavated soil and it is necessary, therefore, to cyclically return it to the surface and empty it. Therefore, filling cycles of the excavation tool indicate the excavation steps in which the tool is filled with the excavated soil.
The first excavation step is performed in the virgin soil by making a hole having a depth about equal to the excavation tool.
Once the hole has been started, to prevent the risk of loosening of the cable, the operators of drilling machines of known type proceed with the advancement of the excavation according to the following steps for each filling cycle of the excavation tool:                The excavation tool 15 is descended into the hole by unwinding the cable of the main winch 8 so that the telescopic rods of the string 12 are extracted. The actuation of winch 8 is controlled by actuating a control member, typically a joystick or a dedicated maneuvering manipulator present in the control cabin of the machine.        During the descent of the excavation tool 15 into hole partially made, the operator must check the indicator of the depth reached by the excavation tool 15, commonly called depth gauge, present in the cabin. Before the excavation tool 15 reaches the bottom of the excavation, that is the depth reached during the previous filling cycle of the tool, the operator slows the descent of the tool by acting on the joystick that controls the unwinding of the cable from the winch. The descent is slowed down until it is stopped as close as possible to the bottom.        When the operator stops the descent, if the excavation tool 15 is in the proximity of the bottom of the excavation and cable 9 is tensioned, no correction maneuver is required. If instead the excavation tool 15 has reached the bottom leaning thereon and cable 9 is loose and no longer substantially straight in the vertical direction, the operator must correct the configuration of cable 9 by acting on the joystick and rewinding the winch a little until cable 9 is tensioned again. The operator in the cabin can visually check if cable 9 is tensioned, as it exits the excavation and continues towards head 7 on which it is returned.        The operator activates the “winch release mode” via a command, preferably by pedal, present in the cabin. In this mode, the main winch 8 is left only slightly braked. For example in these conditions, a pull of 600-700 kg induced by a load on the cable is sufficient to make the winch turn, thus overcoming the braking. In this condition, i.e. in “winch release mode” active, the excavation tool 15 leans on the bottom due to its own weight and the weight of the rods which is much higher than the pull sufficient to unwind the winch.        With the excavation tool 15 resting on the bottom of the excavation, the operator controls the rotation of the rods, preferably without applying thrust to the tool. The rotation of the rods is activated through a joystick in the cabin that controls the rotation of rotary 10. During this rotation, the “winch release mode” is still active. The excavation tool 15, due to its structure, of the screw type in the case of auger or with ploughshare lower opening in the case of buckets, tends to advance in the soil in screwing and thus tensions the inner rod 12A, which slides downwards, and consequently cable 9, which remains tensioned during the advance of the tool. The advancement is at most equal to the height of the tool itself.        
If a thrust force must be exerted on the tool to advance it, it is necessary that all the rods of string 12 are mutually engaged and that the outermost rod 12B is engaged with respect to the sleeve of the rotary. Thereafter, rotary 10 is moved downwards with the pull push system 11 of a known type and the excavation is executed.                The excavation tool 15 is extracted by maneuvering the winding of cable 9 through the rotation of the main winch 8. This winding returns the rods, packing them up to make the tool and the same rods exit from the excavation.        
The drilling machines of known type have the drawback that it is difficult for the operator to be able to maintain cable 9 tensioned during all the excavation steps. Therefore, frequently problems occur due to the loosening of cable 9.
In fact, for example, if the operator is late in stopping the descent into the excavation, the excavation tool 15 touches the bottom of the excavation, thus stopping, and cable 9 due to the inertia due to the weight of all the suspended section of cable that goes from the swivel joint 14 to the pulley in head 7, tends to continue to unwind for a short stretch, thus dragging the main winch 8 into rotation. Few centimetres of excessive unwinding are sufficient to create the problem of the loosening of cable 9, i.e. of removal from the straight configuration of the cable itself, and said problem gets worse if, once the tool has reached the bottom, the operator continues to keep the joystick that controls the unwinding of the cable actuated. In this case, there may be tens of centimetres of excess unwound cable.
The loosening of the cable can occur also in the case that the excavation tool 15 encounters obstacles during the descent in the stretch of hole previously excavated. For example, the excavation tool 15 may rest on a portion of collapsed wall. In this case, the excavation tool 15 stops or slows down its descent speed with respect to the unwinding speed of cable 9 from winch 8. This leads to a reduction of tension on the cable, whereby it tends to bend.
When cable 9 is loosened, the swivel joint 14 which connects the inner rod 12A to cable 9 is arranged inclined, as shown in FIG. 2B, until it rests against on the inner wall of the outer rod 12B. In this condition, the swivel joint 14 does not operate properly and does not perform its function of releasing cable 9 from the rotation of rods 12. If in this condition, i.e. with inclined swivel joint 14, the operator controls the rotation of the rods without having first proceeded to tension the cable by rewinding it on winch 8, it happens that both half-joints 14A and 14B of the swivel joint 14 revolve together with rod 12A, and thus the upper half-joint 14B performs an eccentric trajectory with respect to the longitudinal axis of the rods. This eccentric movement of the upper half-joint 14B causes the twisting of the cable, which leads to rapid wear and tear of the cable itself.
In addition, the loosening of cable 9 and its arrangement in non-straight configuration can cause vibrations during the rotation of the string of rods 12 and thus an oscillation of the rods that may impair the correct execution of the excavation.
An excessive loosening of cable 9 can also cause an incorrect winding of cable 9 itself, which being arranged incorrectly on the drum may undergo early wear or plastic deformation that lead to breakage.